Tuesday, June 18, 2019

[Ichthyology • 2019] Mollisquama mississippiensis • A New Western North Atlantic Ocean Kitefin Shark (Squaliformes: Dalatiidae) from the Gulf of Mexico

Mollisquama mississippiensis
Grace, Doosey, Denton, Naylor, Bart & Maisey, 2019 

A new species of kitefin shark (Squaliformes; Dalatiidae) is described from the Gulf of Mexico (Western North Atlantic Ocean) based on five diagnostic features not seen on the only other known Mollisquama specimen, the holotype of Mollisquama parini Dolganov which was captured in the Eastern South Pacific Ocean. The new species, Mollisquama mississippiensis sp. nov., is distinguished from its congener by a putative pit organ located ventrally just posterior of the lower jaw margin center, photophores irregularly distributed along many areas of the body, 16 distinct ventral-abdominal photophore aggregations, and two differences associated with the dentition. Other potential distinguishing features are 10 fewer vertebrae than Mollisquama parini and six morphometric proportional differences that exceeded +/- 20% from the holotype.

Keywords: Pisces, Mollisquama mississippiensis sp. nov., bioluminescent shark, putative pit organ, synchrotron scans

Figure 1. Mollisquama mississippiensis sp. nov., TU 203676 illustrated to scale in (A) lateral and (B) ventral view.

Mollisquama mississippiensis sp. nov.
 American Pocket Shark

Diagnosis. Differs from the only other described species of Mollisquama, M. parini (Zoological Institute, St. Petersburg, Russia, ZIL-45988), in having a putative pit organ centrally placed just posterior to the lower jaw margin, photophores irregularly distributed along many areas of the body, a series of 16 ventral-abdominal photophore aggregations, upper teeth without a labial-surface ridge (M. parini has a labial-surface ridge), and lower teeth with a weak or absent basal sulcus (M. parini has a deep basal sulcus). The distinguishing external features the pit organ and photophore aggregations were clearly discernable when the new species was captured (Grace et al. 2015) and after preservation. These features were not reported as present on M. parini.

Etymology: The Latin specific epithet is in recognition of the vast North American Mississippi River Basin (Fig. 7); a biologically and geographically rich region that nurtures Gulf of Mexico fauna and unites diverse cultures. The proposed common name is the American Pocket Shark in recognition of the extraordinary Americas of the Western Hemisphere.

Mollisquama mississippiensis sp. nov. is distinguished from M. parini by five features that cannot be accounted for by ontogeny or sexual dimorphism. Additionally, there are 10 fewer vertebrae than M. parini and six morphometric proportional differences that vary from the holotype by +/- 20% that are not affected by ontogenetic allometry for distal features that is often characteristic of squaloid sharks; the vertebral count and morphometric differences are potential distinguishing features. Mollisquama mississippiensis sp. nov. and M. parini were collected from different habitats that are influenced by differing oceanographic conditions–M. parini from an area of the Pacific Ocean known for its isolation and high degree of endemism (Parin et al. 1997). The accession of M. mississippiensis sp. nov. has led to important dalatiid-characterization advances including a considerable range extension for the genus Mollisquama, the first report of a putative pit organ set on a neuromast from a squaliform shark, detailed imagery of the highly specialized pocket gland and confirmation of its bioluminescent properties, a new report of photophores for a dalatiid, and the broadest degree of dalatiid character transformations (eight) based on phylogenetic analysis and character optimization (Denton et al. 2018; two dental, two chondrocranial, three jaw, one muscular). 

Mark A. Grace, Michael H. Doosey, John S. S. Denton, Gavin J. P. Naylor, Henry L. Jr. Bart and John G. Maisey. 2019. A New Western North Atlantic Ocean Kitefin Shark (Squaliformes: Dalatiidae) from the Gulf of Mexico. Zootaxa. 4619(1); 109–120.  DOI: 10.11646/zootaxa.4619.1.4

1 comment:

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